The present invention relates to industrial burners and especially to industrial burners adapted to utilize a variety of fuels, including dehydrated pulverized organic materials.
Large, high capacity fuel burners are generally used in industries requiring drying of various materials. For example, such burners are required for operating large, rotary aggregate dryers and for kiln drying and processing of lime, bauxite, sand, coal, cement, and the like. In the making of asphalt roads, drying units are used for drying the aggregate before mixing with the asphalt.
In drying aggregate, as an example of an application of the fuel burners in consideration, a typical unit may have a rotating, horizontal drum 30 feet in length and 8 feet in diameter. The wet rock is introduced into one end of the drum, carried to the top of the drum and dropped back. The material is gradually carried to the opposite end of the drum and removed by a conveyor. A fuel burner which may have an outlet chamber of from one or more feet in diameter is placed at one end of the drum. The hot gases and air emanating from the burner are directed through the falling aggregate, known as the aggregate curtain, and serves to dry out all moisture from the material. An exhaust fan at the output end of the drum draws the heated air therethrough. The gas temperature at the burning input end may be on the order of 2400 F., dropping to about 350 F. at the opposite end of the drum. In large dryers such as described above, the burners are required to produce as much as 200 million btu's per hour.
In the past, a variety of fuels have been utilized in burners, but by in large, recent burners have used natural gas or fuel oil. In recent years, the absence of certain types of fuels in different parts of the country has resulted in entire manufacturing plants not being able to operate because of the lack of the type of fuel the plant is designed to use. As a result of this, more and more industrial burners are designed to use more than one type of fuel, and may for instance, use pulverized coal and natural gas with the ability to switch from one to the other as price and availability dictate. It has also been suggested in prior years to utilize wood or other organic materials in pulverized form for operating burners. However, when fuel oil and natural gas were less expensive, systems using organic energy were not economically feasible. But, with a rapidly escalating price of oil, industrial burners which utilize pulverized organic materials appear to be more desirable.
In the present invention, organic materials are dehydrated and pulverized to desirable moisture content of approximately twenty percent (20%). The desired particles are then forced at high pressure through pelletizing mills. The result is a pellet about a quarter of an inch in diameter and about three quarters of an inch long (1/4.times.3/4). These pellets then are used in specially designed industrial burners, which may also have the capability of using gas or oil as a back-up fuel. The pellets can be made from any vegetable or organic matter, such as scrapboard chips, hay, sugar cane, left over from forest products industries, municipal refuge and other waste materials that are generally regarded as sources of pollution. The cost of the pellets utilizing various and otherwise waste materials is now competitive with other fuels and in many cases, the cities are now paying to haul organic materials to landfills and to separate and sell the usable material to a pellet manufacturer. The present burner can then take the pelletized material for operating the burners, but in the event that sufficient pelletized material is not available, the burner can alternatively switch from the pellet fuel to gas, or used dried organic material without pelletizing.
A typical U.S. patent which shows the use of pulverized fuel and oil either alone or simultaneously can be seen in U.S. Pat. No. 2,111,980 for a Combustion Apparatus. However, such prior art pulverized fuel burners have utilized pulverized coal and frequently have combined pulverization with gas or oil burners used in combination. Other powdered fuel burners can be seen in U.S. Pat. Nos. 1,618,808 and 3,777,678. These patents suggest using dual walled burners with combustion air being fed between the walls into the combustion chamber. U.S. Pat. No. 4,351,251 shows a burner for dehydrated pulerized organic materials. U.S. Pat. No. 3,391,981 to Voorheis, et al., shows a forced air draft burner for combustable gases having concentric annular air delivery paths and means for spinning air in two paths in opposite directions. The present invention is designed to operate primarily in connection with low density, low mass, fibrous fuels made from various forest products, waste, or reclaimed paper which has been dried and is fed by with air to the burner.
In constrast to the prior art, the present burner is for the specific solid fuel application of burning low density, low mass, fibrous fuels, such as pulverized paper waste or biomass and maintains flame stability while preventing the accumulation of the solid materials by the rotating of the solid material and air entering the combustion chamber in one direction and the rotation of secondary air in the opposite direction. The use of a specially designed gas nozzle maintains substantially 100% burn of the solid fuel by its positioning and feeding into the center of the solid fuel nozzle output. The burner is also capable of operating on gas only, as desired, when there is insufficient solid fuel. The present burner is designed for boilers or furnaces that do not have available hot secondary combustion air, such as applications requiring smaller sized burners which require adjustable flame lengths. The burners can be adjusted for different applications without internal changes to the burner or combustion chamber.